In matrix printers use is made of a bundle of printing wires assembled in a predetermined square or rectangular format and in which certain wires are selected and then displaced longitudinally. Thereafter, displacement of the entire bundle effects printing. The present invention concerns the wires themselves rather than the overall printing arrangement, nevertheless the nature of the printer is such as to dictate the problem which the invention solves.
In effect, the wires are preferably composed of a hard material such as tungsten carbide. In order to use such wires, it is desirable that one end be provided with a suitable cap, preferably of a plastics material and the use of such caps facilitates greatly the longitudinal displacement of the wires within the matrix. The other end of the wire of course is the striking end.
To attach such caps to the ends of the wires it has been customary to mould them over such wires. This in turn necessitates a support arrangement on the wire itself since the cap is of a plastics material very much softer than the wire material and at the same time the wire may be of extremely fine gauge.
In prior art arrangements it has been customary either to form one end of the wire as a loop or alternately to apply a material such as solder or brazing metal to one end. In the first case a problem arises from the nature of the wire material wherewith loop forming is a difficult operation owing to the hardness and brittleness of the wire which as mentioned previously will probably be of a material such as tungsten carbide. Heating would be required and this will alter the wire crystalline structure. In the case where it is desired to apply a drop of metal such as solder or brazing metal this also involves heating the wire and thereby altering its crystalline qualities.
It is the problems in the known type of wires to which the present invention is addressed.